Transformer



June 17, 1941. FQR. DENTREMONT TRANSFORMER Filed March 16, 1940 2Sheets-Sheet l 11 Illllllllllll Fig.2.

Inventor;

is ttorney Fran k I i n R DEntrernomt June 17, 1941.

F. R. D'ENTREMONT I TRANSFORMER Filed March 16, 1940 2 Sheets-Sheet 2Irwverwtor:

D Entremont,

. JMAM, Attomey.

" along the line 2-2 of the Patented June 17, 1941 2,246,167TRANSFORMER. Franklin E. DEntremont, Lynn, Mass, assignor to General NewYork Company, a corporation of Application March 16, 1940, Serial No.324,396 4 Claims. (Cl. 175358) The present invention relates totransformers and more particularly to current transformers of the woundprimary type.

Current transformers are generally connected permanently in seriescircuit with the power lines and accordingly will be subjectedoccasionally to heavy overloads, which may cause damage by mechanicalstresses or by overheating the winding. Heavy current surges occurringon the power line may give rise to mechanical stresses not only throughthe bus connections but also within the transformer itself. Sustainedheavy overloads may cause severe heating of the transformer windings tothe point that the insulation thereof is damaged and with lesseroverloads, even though the transformer may not appear to be damaged, itswindings may have become short-circuited due to overheating thusproducing an incorrect ratio of transformation. Fuse protection cannotbe applied practicably to a current transformer because of its seriesconnection in the line and accordingly, it must be designed so that itwill carry all currents incident to the line.

It is, therefore, an object of this invention to provide a currenttransformer of the wound primary type having a new and improved primaryand terminal structure whereby the tansformer is given great mechanicalstrength and heavy current carrying capacity.

For a consideration of what I believe to be novel and my invention,attention is directed to the following description and the claimsappended thereto taken in connection with the accompanying drawings.

In the drawings Fig. 1 is a side view of a current transformer, partlyin section, con structed in accordance with one form of the invention;Fig. 2 is a view, partly in section, taken transformer shown in Fig. 1but showing the upper primary coil structure in full; Fig. 3 is a viewin perspective of the component parts of the primary winding structurebefore assembly; Fig. 4 is a view of the completed primary assembly; andFig. 5 is a view of the primary assembly with insulation wrappingapplied.

Referring now to Figs. 1 and 2 of the drawings, the transformer includesa rectangular laminated magnetic core II). For obtaining greateraccuracy in the electrical characteristics ofthe transformer, theprimary and secondary windings are divided into two coils each, whichare arranged upon opposite legs of the core structure. The two secondarywinding coils i2 and i3 are relatively wide and are suitably wrappedwith insulation such as varnished cambric, while the surrounding primarycoils I4 and I5, respectively, are covered first with filler pieces l6and I1 and then with wrapping l8 of suitable insulating material. Aninsulating spacer I9 is arranged between the adjacent inner turns of theprimary coils, having been inserted in position before the wrapping l8was applied. The two primary coils are connected in parallel between twoterminal members 20 and 2| extending outwardly from the opposite sidesof the transformer substantially along the axis thereof. The terminalmembers are preferably relatively wide so that they may be securelyfastened to bus bars 22 and 23 in a good heat and current conductingrelation by any suitable means such as bolts 24 and 25.

Referring now to Figs. 3 and 4, the structure of the primary windingcoils will now be described in greater detail. The coils l4 and I5 areof similar configuration and are preformed of relatively wide copperstrap wound flatwise in a single layer as regards the outer surface ofthe cooperating secondary coils. Each coil in this instance comprisestwo turns, that is, two portions 3|, 32, and 33, 34 adapted to extendthrough the window of the core structure and which portions areconnected together by side and cross over portions 35 and 36,respectively. The coil ends, that is, the ends 31, 38, and 39, 40 arebent at right angles to the portions of each coil extending through thecore window and lie parallel with and adjacent to the correspondingstrap is preferably of maximum width, or, of such a width so that theoverall width of the coils is substantially equal to the width of thesecondary coils. A maximum heat radiating surface for the primary coilsis thus provided.

The terminals 20 and 2| are each formed from relatively heavy flatstripsof copper having a width substantially equal to the overall width of thecoils I4 and 55. One end of the terminals is first slotted as indicatedat 4| and 42, respectively, the width of these slots being substantiallyequal to the spacing between the adjacent turns of the primary coils.The bifurcated end portions of each terminal are bent at right angleswith respect to the main terminal portion providing oppositely extendinglugs 43, 44, and 45, 46. The lugs 43, 44 are suitably secured, as bybrazing, fiatwise to the ends 31 and 39 of the coils. l4 and I5, whilelugs 45, 46 are similarly secured to the. other coil ends 38 and 40,

respectively, as shown more clearly in Fig. 4. The ends of the terminalsmay be provided with holes 41 and 48 for cooperatively receiving thefastening bolts 24 and 25.

After the primary windings have been assembled, the insulating spacermember I9 is inserted into the space between the adjacent turns 3|, 32,and 33, 34 of the two primary coils engaging tightly therewith. Thefiller pieces [6 and ll, of insulating material such as pressed paper,are then fitted over the cores and the assembly is wrapped with asuitable insulation, such as crepe paper, the wrapper assembly beingshown in Fig. 5. The secondary coils are then nested concentrically intothe primary coils after which the laminations of the core are stackedthrough coils and fastened together by bolts The transformer may then bethoroughly dried and dipped in an asphaltum insulating compound forfilling any spaces which may exist within the assembly.

The primary coils will possess relatively ical strength so as toconstructed in this manner great rigidity and mechaneii'ectively resistany deformation from their original shape due to any mechanical stresseswhich may be imposed thereupon through the bus bars or other connectionsto the terminals. The lugs 43, M, and 45, 46 extending in oppositedirections from the ends of the terminals and being securely fastened tothe ends of the winding coils will provide suflicient rigidity for theterminals as regards any laterally imposed stresses. Any force actinglongitudinally of the terminals will be transmitted to the portions ofthe primary windings extending through the core windows, but because ofthe fact that the primary coils fit tightly around the secondary coilsthere will be no play which may be taken up by a relative separation ofthe two terminals.

The thermal limit of transformers having a primary coil construction asdescribed is very high due to various design features. The greatestheating will normally take place within the core window due to the factthat no space exists therein for the circulation of air currents. By theconstruction shown, the heat will be readily conducted from the corewindow portions of the primary turns since the terminals are directlyconnected thereto immediately adjacent the window. The broad flatterminals fastened in a good heat conducting relationship to the busbars will in turn carry the heat away from the transformer at a highrate. The cross over portions of the primary winding being near thesurface of the assembly will dissipate heat by radiation to the ambientatmosphere.

The symmetrical arrangement of the coils on the core and the primarycoils closely surrounding the secondary coils reduces the leakage re- I,actance of the transformer to a minimum and tends to improve materiallythe accuracy of the device.

Having described the invention in what I now consider to represent thebest embodiment thereof, I desire to have it understood that theinvention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a transformer having a rectangular magnetic core structure, twosecondary winding coils one being arranged around each of a pair ofopposite core legs, two primary winding coils one surrounding each ofsaid secondary coils, said primary coils each comprising a strapconductor wound fiatwise around the corresponding secondary coil in asingle layer, the ends of said conductor extending through the corewindow andshort distances along opposite sides of said core, a pair ofterminals each having at one end lugs substantially the width of saidconductor extending at right angles on opposite sides thereof, said lugsbeing secured to said ends of said primary coil and an insulating memberarranged in the window of said core and separating said two primarycoils.

2. A transformer comprising a magnetic core structure, two secondarywinding coils one surrounding each of a pair of opposite legs ofsaidcore, two primary winding coils one surrounding each of said secondarycoils, said primary coils each comprising a relatively wide strapconductor extending fiatwise around the corresponding secondary coil ina single layer to a Width substantially equal to the width of saidsecondary coils, the ends of said conductor extending through the corewindow and terminating along the opposite sides of said core, and a pairof terminals each having at one end a pair of lugs extending at rightangles on opposite sides of said terminals, said lugs being rigidlysecured flatwise to corresponding ends of each of said primary coils.

3. In a transformer having a magnetic core structure and a secondarywinding having portions arranged around opposite portions of said corestructure, a primary winding comprising a strap conductor wound flatwisein a single layer around said secondary winding providing a plurality ofturns through the window of said core structure, the ends of said turnsextending along opposite sidesof said core, and a pair of terminalshaving portions extending across the window of said core on oppositesides thereof, said portions being secured with respect to spacedportions of said primary winding, said ends of said turns beingconnected to corresponding terminal portions.

4. In a current transformer having a rectangular magnetic core and apair of secondary windings arranged around opposite legs of said core, apair of symmetrical and parallel connected primary windings arrangedaround said secondary windings, said primary windings each comprising aplurality of turns of a relatively wide conductor wound flatwise in asingle layer, the corresponding ends of the two windings extending inopposite directions on opposite sides of the window of said core,relatively wide terminal members having a pair of lugs at one endextending substantially across the core window, the lugs of eachterminal member being rigidly connected to corresponding winding ends.

FRANKLIN R. D'ENTREMONT.

